Study on the mechanism of hydrogen production by catalytic pyrolysis of bagasse over CaO/Na<sub>2</sub>CO<sub>3</sub>
Songsong Zhang, Daokuan Liang, Xiaofeng Li, Yaohui Fan, Heyi Huang, Xiao He, Lin Wang, Zhaoying Li, Yong Dong
Abstract
As a major type of agricultural waste, bagasse is rich in volatile matter and low in ash, making it an ideal raw material for thermochemical conversion to hydrogen-rich gas. In this study, an <italic>ex-situ</italic> microwave-assisted catalytic pyrolysis technique was used. CaO and Na<sub>2</sub>CO<sub>3</sub> and their mixed catalysts in different ratios were selected for the experiments at 550 °C. The aim is to optimize both the hydrogen yield and concentration of the components to produce high-quality fuel. Thermogravimetric analysis (TG/DTG) revealed the influence of the catalysts: Na<sub>2</sub>CO<sub>3</sub> significantly promotes low-temperature deoxygenation, and CaO can effectively adsorb CO<sub>2</sub>. Molecular dynamics simulations showed that elevated temperatures promote carbon chain breakage, but too high a temperature (2,500 K) may lead to a carbonization cascade reaction, which inhibits bond breakage. The gas-phase products indicate that the mixed catalyst is most effective at a ratio of CaO : Na<sub>2</sub>CO<sub>3</sub> of 1:3, achieving the highest H<sub>2</sub> yield (maximum 17.26%) along with significant hydrocarbon generation inhibition (24.90%), and CO content reduction (23.45%). Catalyst characterization confirmed the presence of CaCO<sub>3</sub> in the mixed catalysts after pyrolysis. The CaO : Na<sub>2</sub>CO<sub>3</sub> = 1:3 catalyst was found to have a unique fibrous structure and a microporous network. Raman spectroscopy reveals the ordering of the carbon structure and differences in functional groups under the action of different catalysts. This study provides a theoretical basis for further optimizing the pyrolysis process of bagasse, and helps improve the conversion efficiency of biomass energy.